ive just found some in my firewood pile, (smaller branches admittedly 4") which has been outside in all weathers for about a year, and after storing in the shed for a few weeks they're still a little green, but great to turn. i imagine if your logs were stored properly under cover a year or so should do it. or alternatively if bowls are the intended target turn roughly to shape whilst wet to bout an inch thick, then go for the store in newspaper or plastic/ paper bag method, or even microwave. (search the forum, you'll find plenty of (differing)opinions.) to reduce drying time.
hth